The semiconductor device, such as a semiconductor laser diode, which has been used in various fields, makes increased heat generation during operation, and thus heat sinks are generally used for cooling it.
The development of high performance semiconductor devices and the like in recent years, such as one with high brightness and/or high output power, requires higher cooling properties in a heat sink. The durability of such cooling properties are also requires in a heat sink, such that the heat sink stably performs its capability of dissipation of heat from heat-generating devices, such as a semiconductor device, during its long lifetime. To meet these demands, various types of heat sinks are developed.
While the capabilities of the heat sink being further improved, there is a tendency for it to increase in size, thickness, etc., and such heat sink cannot be suitable for some of recent semiconductor devices and the like that become further small in size.
Accordingly, to solve such problems, WO 00/11922 discloses a structure of heat sink 100 as illustrated with the cross-section view in FIG. 9.
This heat sink 100 comprises base members 110, 120 and 130 that are mainly made of copper in plate-like shapes as illustrated with the cross-section view in FIG. 9a. After the base members being assembled as illustrated with the cross-section view in FIG. 9b, and being bonded by means of adhesion or the like, interspace 150 is formed inside the assembled base members, in which the interspace 150 has boundary of the surfaces of the base members 110, 120 and 130. A through hole 160 is also formed, which communicates one part of interspace 150 created with the base members 110 and 120 to the other part of interspace 150 created with the base members 120 and 130. By allowing a coolant to flow into and to flow out of the thus formed interspace 150 and through hole 160, a semiconductor device 170, such as a semiconductor laser diode, which is mounted onto the outer surface of the base members 110, is cooled by the thus formed heat sink 100.
In the heat sink 100, during a long term circulation of coolant going through the interspace of the heat sink with inflow and outflow, a physical and/or chemical phenomenon such as corrosion or erosion-corrosion occurs on the inner surfaces of the base members 110, 120 and 130 that are in contact with the coolant.
Here, the erosion-corrosion means a mode of corrosion in which a chemical corrosion is accompanied by erosion with mechanical degradation. In the case of the heat sink 100, the chemical corrosion is caused by a chemical reaction between the coolant and the base members 110, 120 and 130, while the mechanical degradation is caused by a mechanical contact of the substances that are contained in the flowing coolant with the inner surfaces of the base members.
The corrosion or erosion-corrosion occurred as mentioned above, causes liquid leakage of the heat sink 100 or reduction of the flow amount of the coolant that is going through the heat sink. As the material for the base members 110, 120 and 130, Cu is generally used, which has excellent thermal conductivity and is relatively low in price. In such an instance, however, corrosion products such as verdigris are formed during a long time circulation of the coolant. The corrosion products cause clogging, and thus lower the flow amount of the coolant that is going through the coolant. Such reduction of the flow amount remarkably decreases the cooling performance of the heat sink.
Further, in a case where a semiconductor laser diode 170 is mounted onto the heat sink 100 to be cooled down, the semiconductor laser diode functions as an electrode (anode or cathode) while the heat sink 100 itself functions as another electrode (cathode or anode). In such case, because of the electric current flowing through the materials of the heat sink 100, as well as through the semiconductor laser diode, the inducement of electrolytic etching is tend to occur. The result from such electrolytic etching is the deformation or clogging of the flow path, further resulting in the reduction of the flow amount of the coolant that is going through the heat sink. In complementing of the reduction of the flow amount by raising the liquid pressure or the like, such pressure often damages the inner surfaces of the heat sink, causing liquid leakage, etc.
To prevent the above problem of the degradation in quality for cooling performance, a coating treatment of the interspace 150 formed inside the heat sink 100, may sometimes be made after bonding of the base members 110, 120 and 130. However, it has been difficult to make a precise coating in an appropriate thickness on the surfaces of the base members creating the interspace 150, in which the coolant flows, so that area of the cross section of the flow path would be in constant shape.